Conventionally, as a wire winding method for a rotor of a direct-current motor, a technique described in JP 10-285854 A (PTL 1) is known.
A direct-current motor in PTL 1 includes an armature core (armature) having a rotating shaft outer circumferential portion provided at a center thereof with a through hole fitted to a rotating shaft and multiple approximately-T-shaped magnetic pole portions formed in a radial direction from this rotating shaft outer circumferential portion (paragraph 0012). In this armature core, slots are formed between the adjacent approximately-T-shaped magnetic pole portions to constitute multiple slots in a circumferential direction (paragraph 0013).
PTL 1 also discloses the following configuration (paragraphs 0013 to 0020).
The armature core has a four-pole thirteen-slot configuration, and armature coils are wound by means of wave winding. Specifically, each coil is wound to interpose two slots between the approximately-T-shaped magnetic pole portions arranged on both sides of the two slots in the circumferential direction to stride over the approximately-T-shaped magnetic pole portions. That is, each coil is wound to stride over an arbitrary slot (first slot) and a second slot located at a position reached by skipping two slots from the first slot. The number of armature coils is thirteen, and relationship between respective armature coils C1 to C13 and slots S1 to S13 through which the coils are wound is as follows. The first armature coil C1 is wound to stride over the slots S1 and S4, the second armature coil C2 is wound to stride over the slots S7 and S10, the third armature coil C3 is wound to stride over the slots S13 and S3, the fourth armature coil C4 is wound to stride over the slots S6 and S9, the fifth armature coil C5 is wound to stride over the slots S12 and S2, the sixth armature coil C6 is wound to stride over the slots S5 and S8, the seventh armature coil C7 is wound to stride over the slots S11 and S1, the eighth armature coil C8 is wound to stride over the slots S4 and S7, the ninth armature coil C9 is wound to stride over the slots S10 and S13, the tenth armature coil C10 is wound to stride over the slots S3 and S6, the eleventh armature coil C11 is wound to stride over the slots S9 and S12, the twelfth armature coil C12 is wound to stride over the slots S2 and S5, and the thirteenth armature coil C13 is wound to stride over the slots S8 and S11.